The electrochemical art desires to improve the operating characteristics of electrolytes used in electrochemical devices. In devices such as batteries, capacitors and displays, these electrolytes additionally must be highly conductive in order to allow useful current flux during use. In addition, the electrolyte must be chemically and electrochemically stable towards both cathode and anode materials.
When a potential is applied across an electrolytic cell containing a conventional electrolyte, the cations and anions migrate to the negative and positive electrodes, respectively, thereby forming a charge gradient in the electrolyte. This effect is particularly pronounced in solid polymer electrolyte (SPE) materials which, due to the rigid macromolecular structure of the electrolyte, has considerably reduced cationic mobility and reduced overall ionic mobility. Attempts have been made to prepare a solid polymer electrolyte in which only one of the charged species has mobility by fixing the anions to the polymeric chain so that only the cations are mobile. While immobilizing the anion on the polymer electrolyte chain has the effect of preventing migration during use, it has the additional undesirable effect of reducing cation mobility (and hence conductivity) because of the high affinity of the cation to the immobilized anion. Thus, it is desirable to improve the operating characteristics of electrolytes and to overcome these and other operational limitations inherent in electrochemical devices. One way of overcoming the limitations of the materials currently used in the electrochemical art is to develop and investigate new materials for their potential application in electrochemical cells.
Interlocking molecular systems which self-assemble have been the object of much recent interest and investigation; however, they have not been examined for use in electrochemical cells. Interlocking molecular systems include rotaxane complexes formed by noncovalent interactions between a linear molecule and a cyclic molecule which results in the "threading" of the cyclic molecule or "bead" onto the linear molecule "string". Sterically large terminal groups on the linear molecular string prevent the decomplexation or "de-threading" of the cyclic molecular "beads". Recently, the synthesis and characterization of self-assembling "rotaxanes" have been reported. The interested reader is directed to Stoddart ("Making Molecules to Order" Chemistry in Britain, 714-718, Aug., 1991), Stoddart ("Cyclodextrins, Off-the-Shelf Components for the Construction of Mechanically Interlocked Molecular Systems" Angew. Chem. Int. Ed. Eng. 31(7), 846-8, 1992), Rao et al. ("Self-Assembly of a Threaded Molecular Loop" J. Am. Chem. Soc. 112, 3614-5, 1990) and Harada et al. ("Preparation and Characterization of Polyrotaxanes Containing Many Threaded Cyclorotaxanes" J. Org. Chem. 58, 7524-8, 1993) for further information.
Many rotaxane complexes function as "molecular shuttles" by moving back and forth between identical stations along the length of the linear polymer or molecule. Research directed by Stoddart has succeeded in producing a rotaxane complex including a cyclic molecule (made up of two bipyridinium units and two bridging p-xylyl spacers) which moves back and forth between aromatic sites on a linear polyether string (See, "Molecular Shuttle: Prototype for molecular machine" C&EN, 4-5 (Jul. 1, 1991)). The shuttle may be activated by chemical and electrochemical triggers (See, "A Chemically and Electrochemically Switchable Molecular Shuttle" Nature 369, 133-7 (May 12, 1994)); however, a practical application for such molecules has yet to be proposed.
While these interlocking molecular systems have generated much excitement in the scientific community because of their ability to self-assemble and self-replicate at a molecular level, practical applications utilizing these self-assembling complexes have not been rapidly forthcoming.
It is the object of the present invention to provide a molecular complex which can be used in an electrolyte. It is a further object of the invention to provide a molecular complex which exhibits improved conductivity and ion transport. It is a further object of the present invention to provide an electrolyte exhibiting improved conductivity and ion transport. It is yet a further object of the present invention to provide a precursor which improves the control of the nature of the interface between the electrode surface and the solution. It is yet a further object of the present invention to utilize rotaxane complexes in electrochemical and electrolytic devices.